This invention relates to certain monocyclopentadienyl titanium compounds, to a catalyst system comprising a monocyclopentadienyl titanium compound and an alumoxane, and to a process using such catalyst system for the production of polyolefins, particularly ethylene-xcex1-olefin copolymers having a high molecular weight and high level of xcex1-olefin incorporation. The catalyst system is highly active at low ratios of aluminum to the titanium metal, hence catalyzes the production of a polyolefin product containing low levels of catalyst metal residue.
This invention relates to the discovery of various catalyst ligand structure affects which are reflected in the activity of the catalyst system and in the physical and chemical properties possessed by a polymer produced with a monocyclopentadienyl titanium metal catalyst system. Accordingly, various species within the general class of monocyclopentadienyl titanium catalyst as disclosed by commonly-owned U.S. patent application Ser. No. 07/581,841, have been discovered to be vastly superior in terms of the ability of such species to produce ethylene-xcex1-olefin copolymers of high molecular weight with high levels of xcex1-olefin comonomer incorporation and at high levels of catalyst productivity.
As is well known, various processes and catalysts exist for the homopolymerization or copolymerization of olefins. For many applications it is of primary importance for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. A high weight average molecular weight, when accompanied by a narrow molecular weight distribution, provides a polyolefin or an ethylene-xcex1-olefin copolymer with high strength properties.
Traditional Ziegler-Natta catalyst systemsxe2x80x94a transition metal compound cocatalyzed by an aluminum alkylxe2x80x94are capable of producing polyolefins having a high molecular weight but a broad molecular weight distribution.
More recently a catalyst system has been developed wherein the transition metal compound has two or more cyclopentadienyl ring ligandsxe2x80x94such transition metal compound being referred to as a metallocenexe2x80x94which catalyzes the production of olefin monomers to polyolefins. Accordingly, metallocene compounds of a Group IV B metal, particularly, titanocenes and zirconocenes, have been utilized as the transition metal component in such xe2x80x9cmetallocenexe2x80x9d containing catalyst system for the production of polyolefins and ethylene-xcex1-olefin copolymers. When such metallocenes are cocatalyzed with an aluminum alkylxe2x80x94as is the case with a traditional type Ziegler-Natta catalyst systemxe2x80x94the catalytic activity of such metallocene catalyst system is generally too low to be of any commercial interest.
It has since become known that such metallocenes may be cocatalyzed with an alumoxanexe2x80x94rather than an aluminum alkylxe2x80x94to provide a metallocene catalyst system of high activity for the production of polyolefins.
The zirconium metallocene species, as cocatalyzed or activated with an alumoxane, are commonly more active than their hafnium or titanium analogues for the polymerization of ethylene alone or together with an xcex1-olefin comonomer. When employed in a non-supported formxe2x80x94i.e., as a homogeneous or soluble catalyst systemxe2x80x94to obtain a satisfactory rate of productivity even with the most active zirconium species of metallocene typically requires the use of a quantity of alumoxane activator sufficient to provide an aluminum atom to transition metal atom ratio (A1:(trademark)) of at least greater than 1000:1; often greater than 5000:1, and frequently on the order of 10,000:1. Such quantities of alumoxane impart to a polymer produced with such catalyst system an undesirable content of catalyst metal residue, i.e., an undesirable xe2x80x9cashxe2x80x9d content (the nonvolatile metal content). In high pressure polymerization procedures using soluble catalyst systems wherein the reactor pressure exceeds about 500 bar only the zirconium or hafnium species of metallocenes may be used. Titanium species of metallocenes are generally unstable at such high pressures unless deposited upon a catalyst support.
A wide variety of Group IV B transition metal compounds have been named as possible candidates for an alumoxane cocatalyzed catalyst system. Although bis(cyclopentadienyl) Group IV B transition metal compounds have been the most preferred and heavily investigated for use in alumoxane activated catalyst systems for polyolefin production, suggestions have appeared that mono and tris(cyclopentadienyl) transition metal compounds may also be useful. See, for example U.S. Pat. Nos. 4,522,982; 4,530,914 and 4,701,431. Such mono(cyclopentadienyl) transition metal compounds as have heretofore been suggested as candidates for an alumoxane activated catalyst system are mono(cyclopentadienyl) transition metal trihalides and trialkyls.
More recently, International Publication No. WO 87/03887 describes the use of a composition comprising a transition metal coordinated to at least one cyclopentadienyl and at least one heteroatom ligand as a transition metal component for use in an alumoxane activated catalyst system for xcex1-olefin polymerization. The composition is broadly defined as a transition metal, preferably of Group IV B of the Periodic Table, which is coordinated with at least one cyclopentadienyl ligand and one to three heteroatom ligands, the balance of the transition metal coordination requirement being satisfied with cyclopentadienyl or hydrocarbyl ligands. Catalyst systems described by this reference are illustrated solely with reference to transition metal compounds which are metallocenes, i.e., bis(cyclopentadienyl) Group IV B transition metal compounds.
Even more recently, at the Third Chemical Congress of North American held in Toronto, Canada in June 1988, John Bercaw reported upon efforts to use a compound of a Group III B transition metal coordinated to a single cyclopentadienyl heteroatom bridged ligand as a catalyst system for the polymerization of olefins. Although some catalytic activity was observed under the conditions employed, the degree of activity and the properties observed in the resulting polymer product were discouraging of a belief that such monocyclopentadienyl transition metal compound could be usefully employed for commercial polymerization processes.
Although the metallocene/alumoxane catalyst system constituted an improvement relative to a traditional Ziegler-Natta catalyst system, a need existed for discovering catalyst systems that permit the production of higher molecular weight polyolefins and desirably with a narrow molecular weight distribution. Further desired was a catalyst which, within reasonable ranges of ethylene to xcex1-olefin monomer ratios, will catalyze the incorporation of higher contents of xcex1-olefin comonomers in the production of ethylene-xcex1-olefins copolymers.
Commonly owned copending U.S. application Ser. No. 07/581,841, now U.S. Pat. No. 5,096,867, filed Sep. 13, 1990. disclosed the discovery of a class of monocyclopentadienyl Group IV B transition metal compounds which, when activated with an alumoxane, may be employed as a catalyst system in solution, slurry or bulk phase polymerization procedure to produce a polyolefin of high weight average molecular weight and relatively narrow molecular weight distribution.
The xe2x80x9cGroup IV B transition metal componentxe2x80x9d of the catalyst system disclosed in application Ser. No. 581,841 is represented by the formula: 
wherein:
M is Zr, Hf or Ti in its highest formal oxidation state (+4, d0 complex);
(C5H5xe2x88x92yxe2x88x92xRx) is a cyclopentadienyl ring which is substituted with from zero to five substituent groups R, xe2x80x9cxxe2x80x9d is 0, 1, 2, 3, 4 or 5 denoting the degree of substitution, and each substituent group R is, independently, a radical selected from a group consisting of C1-C20 hydrocarbyl radicals, substituted C1-C20 hydrocarbyl radicals wherein one or more hydrogen atoms is replaced by a halogen radical, an amido radical, a phosphido radical, and alkoxy radical or any other radical containing a Lewis acidic or basic functionality, C1-C20 hydrocarbyl-substituted metalloid radicals wherein the metalloid is selected from the Group IV A of the Periodic Table of Elements; halogen radicals, amido radicals, phosphido radicals, alkoxy radicals, alkylborido radicals or any other radical containing Lewis acidic or basic functionality; or (C5H5xe2x88x92yxe2x88x92xRx) is a cyclopentadienyl ring in which at least two adjacent R-groups are joined forming a C4-C20 ring to give a saturated or unsaturated polycyclic cyclopentadienyl ligand such as indenyl, tetrahydroindenyl, fluorenyl or octahydrofluorenyl;
(JRxe2x80x2zxe2x88x92ixe2x88x92y) is a heteroatom ligand in which J is an element with a coordination number of three from Group V A or an element with a coordination number of two from Group VI A of the Periodic Table of Elements, preferably nitrogen, phosphorus, oxygen or sulfur, and each Rxe2x80x2 is, independently a radical selected from a group consisting of C1-C20 hydrocarbyl radicals, substituted C1-C20 hydrocarbyl radicals wherein one or more hydrogen atoms are replaced by a halogen radical, an amido radical, a phosphido radical, an alkoxy radical or any other radical containing a Lewis acidic or basic functionality, and xe2x80x9czxe2x80x9d is the coordination number of the element J;
each Q may be independently any univalent anionic ligand such as a halide, hydride, or substituted or unsubstituted C1-C20 hydrocarbyl, alkoxide, aryloxide, amide, arylamide, phosphide or arylphosphide, provided that where any Q is a hydrocarbyl such Q is different from (C5H5xe2x88x92yxe2x88x92xRx), or both Q together may be an alkylidene or a cyclometallated hydrocarbyl or any other divalent anionic chelating ligand;
xe2x80x9cyxe2x80x9d is 0 or 1 when w is greater than 0; y is 1 when w is 0; when xe2x80x9cYxe2x80x9d is 1, T is a covalent bridging group containing a Group IV A or V A element such as, but not limited to, a dialkyl, alkylaryl or diaryl silicon or germanium radical, alkyl or aryl phosphine or amine radical, or a hydrocarbyl radical such as methylene, ethylene and the like;
L is a neutral Lewis base such as diethylether, tetraethylammonium chloride, tetrahydrofuran, dimethylaniline, aniline, trimethylphosphine, n-butylamine, and the like; and xe2x80x9cwxe2x80x9d is a number from 0 to 3. L can also be a second transition metal compound of the same type such that the two metal centers M and Mxe2x80x2 are bridged by Q and Qxe2x80x2, wherein Mxe2x80x2 has the same meaning as M and Qxe2x80x2 has the same meaning as Q. Such dimeric compounds are represented by the formula: 
The alumoxane component of the catalyst may be represented by the formulas: (R3xe2x80x94Alxe2x80x94O)m; R4(R5xe2x80x94Alxe2x80x94O)mxe2x80x94AIR62 or mixtures thereof, wherein R3-R6 are, independently, a C1-C5 alkyl group or halide and xe2x80x9cmxe2x80x9d is an integer ranging from 1 to about 50 and preferably is from about 13 to about 25.
Catalyst systems may be prepared by placing the xe2x80x9cGroup IV B transition metal componentxe2x80x9d and the alumoxane component in common solution in a normally liquid alkane or aromatic solvent, which solvent is preferably suitable for use as a polymerization diluent for the liquid phase polymerization of an olefin monomer.
As further disclosed in, U.S. application Ser. No. 07/581,841, filed Sep. 13, 1990, now U.S. Pat. No. 5,096,867, that class of the Group IV B transition metal component wherein the metal is titanium have been found to impart beneficial properties to a catalyst system which are unexpected in view of what is known about the properties of bis(cyclopentadienyl) titanium compounds which are cocatalyzed by alumoxanes. Whereas titanocenes in their soluble form are generally unstable in the presence of aluminum alkyls, the monocyclopentadienyl titanium metal components, particularly those wherein the heteroatom is nitrogen, generally exhibit greater stability in the presence of aluminum alkyls, higher catalyst activity rates and higher xcex1-olefin comonomer incorporation.
Further, the titanium class of the Group IV B transition metal component catalyst of the invention described by application Ser. No. 07/581,841 filed Sep. 13, 1990, now U.S. Pat. No. 5,096,867, generally exhibit higher catalyst activities and the production of polymers of greater molecular weight and xcex1-olefin comonomer contents than catalyst systems prepared with the zirconium or hafnium species of the Group IV B transition metal component.
This invention comprises the discovery of a subgenus of monocyclopentadienyl titanium compounds which, by reason of the presence therein of ligands of a particular nature, provide a catalyst of greatly improved performance characteristics compared to other members of the genus of monocyclopentadienyl titanium compounds as described in copending U.S. application Ser. No. 07/581,841 filed Sep. 13, 1990, now U.S. Pat. No. 5,096,867. The subgenus of monocyclopentadienyl titanium catalyst most preferred is that wherein the heteroatom ligand is an amido group, the nitrogen atom of which is bridged through a bridging group (T) to the cyclopentadienyl ring and wherein the nitrogen atom is covalently bonded through a 1xc2x0 or 2xc2x0 carbon atom to an alicyclic or aliphatic hydrocarbyl group. Herein a 1xc2x0 carbon atom is one which is methyl or a carbon atom which is bonded to only one other carbon atom; a 2xc2x0 carbon atom is one which is bonded to only two other carbon atoms, and a 3xc2x0 carbon atom is bonded to three other carbon atoms. Preferably the alicyclic or aliphatic hydrocarbyl group has three or more carbon atoms and is bonded to the nitrogen atom through a 2xc2x0 carbon atom, most preferably the hydrocarbyl group is alicyclic. Monocyclopentadienyl titanium compounds within this subgenus have been discovered to produce a highly productive catalyst system which produces an ethylene-xcex1-olefin copolymer of significantly greater molecular weight and xcex1-olefin comonomer content as compared with other species of monocyclopentadienyl titanium compounds when utilized in an otherwise identical catalyst system under identical polymerization conditions. Further, within this subgenus of titanium compounds it has been found that the nature and degree of substitution groups (R) of the cyclopentadienyl ring can be varied to produce a catalyst system having a xe2x80x9ccatalyst reactivity ratio (r1)xe2x80x9d which may be varied from a high to a low value as may be most desired to best suit the catalyst system to a particular type of polymerization process. Particularly it has been found that as the number of substituents/(R), which are preferably hydrocarbyl substituents, increases the reactivity ratio (r1) decreases, the lowest reactivity ratios being obtained by a titanium compound having a tetrahydrocarbyl substituted cyclopentadienyl group, preferably a tetramethylcyclopentadienyl group.
A typical polymerization process of the invention comprises the steps of contacting ethylene and a C3-C20 xcex1-olefin alone, or with other unsaturated monomers including C3-C20 xcex1-olefins, C4-C20 diolefins, and/or acetylenically unsaturated monomers with a catalyst comprising, in a suitable polymerization diluent, a monocyclopentadienyl titanium compound as described above; and a methylalumoxane in an amount to provide a molar aluminum to titanium metal ratio of from about 1:1 to about 20,000:1 or more; and reacting such monomers in the presence of such catalyst system at a temperature of from about xe2x88x92100xc2x0 C. to about 300xc2x0 C. for a time of from about 1 second to about 10 hours to produce a copolymer having a weight average molecular weight of from about 1,000 or less to about 5,000,000 or more and a molecular weight distribution of from about 1.5 to about 15.0.
The disclosure of U.S. application Ser. No. 07/581,841, filed Sep. 13, 1990, now U.S. Pat. No. 5,096,867, is hereby incorporated by reference.
As disclosed in U.S. application Ser. No. 07/581,841 filed Sep. 13, 1990, now U.S. Pat. No. 5,096,867, wherein it is desired to produce an xcex1-olefin copolymer which incorporates a high content of xcex1-olefin, the class of Group IV B transition metal compound preferred is one of titanium. The most preferred class of titanium metal compounds are represented by the formula: 
wherein Q, L, Rxe2x80x2, R, xe2x80x9cxxe2x80x9d and xe2x80x9cwxe2x80x9d are as previously defined and R1 and R2 are each independently a C1 to C20 hydrocarbyl radicals, substituted C1 to C20 hydrocarbyl radicals wherein one or more hydrogen atom is replaced by a halogen atom; R1 and R2 may also be joined forming a C3 to C20 ring which incorporates the silicon bridge.
Among this class of titanium compounds various substituent and ligand affects have been discovered which significantly affect the properties of a catalyst system. The nature and degree of substitutions (R) in the cyclopentadienyl ring was found to significantly influence the catalyst ability to incorporate xcex1-olefin comonomers when producing an ethylene-xcex1-olefin copolymer. For the greatest amount of comonomer incorporation, the cyclopentadienyl ring should be fully substituted (x=4) with hydrocarbyl groups (R), most preferably methyl groups. This affect is demonstrated by a comparison between Examples 83 to 85. Next, the nature of the Rxe2x80x2 ligand of the amido group significantly influences the capability of a catalyst to incorporate xcex1-olefin comonomer. Amido group Rxe2x80x2 ligands which are aliphatic or alicyclic hydrocarbyl ligands bonded to the nitrogen atom through a 1xc2x0 or 2xc2x0 carbon atom provide for a greater degree of xcex1-olefin comonomer incorporation than do Rxe2x80x2 groups bonded through a 3xc2x0 carbon atom or bearing aromatic carbon atoms. Further, wherein the Rxe2x80x2 ligand is bonded to the nitrogen atom through a 2xc2x0 carbon atom, the activity of the catalyst is greater when the Rxe2x80x2 substituent is alicyclic than when Rxe2x80x2 is bonded to the nitrogen through a 1xc2x0 carbon atom of an aliphatic group of identical carbon number. With regard to an alicyclic hydrocarbyl Rxe2x80x2 ligand it has been found that as the number of carbon atoms thereof increases the molecular weight of the ethylene-xcex1-olefin copolymer increases while the amount of xcex1-olefin comonomer incorporated remains about the same or increases. Further, as the carbon number of the alicyclic hydrocarbyl ligand increases the productivity of the catalyst system increases. This is demonstrated by Examples 71-76. Accordingly, the Rxe2x80x2 ligand most preferred is cyclododecyl (C12H23).
The affects of the bridging group ligands R1 and R2 has been found to be of less significance. The nature of the R1 and R2 ligands exerts a small effect upon the activity of a catalyst. For greatest catalyst activity the R1 and R2 ligands are preferably alkyl, most preferably methyl. The Q anionic ligands of the transition metal have not been observed to exert any particular influence on the catalyst or polymer properties, as demonstrated by comparison of Examples 71 and 86. Accordingly, as a convenience in the production of the transition metal component the Q ligands are preferably chlorine or methyl.
The compounds most preferred for reasons of their high catalyst activity in combination with an ability to produce high molecular weight ethylene-xcex1-olefin copolymers of high comonomer contents is represented by the formula: 
wherein R1 and R2 are each independently a C1 to C6 hydrocarbyl radical, each Q is independently a halide or aikyl radical, Rxe2x80x2 is an aliphatic or an alicyclic hydrocarbyl radical of the formula (CnH2n+b) wherein xe2x80x9cnoxe2x80x9d is a number from 3 to 20 and xe2x80x9cbxe2x80x9d is +1 in which case the ligand is aliphatic or xe2x88x921 in which case the ligand is alicyclic. Of these compounds, the most preferred is that compound wherein R1 and R2 are methyl, each Q is chlorine or methyl, n is 12, and the hydrocarbyl radical is alicyclic (i.e., b is xe2x88x921). Most preferred is that compound wherein the (CnH2nxe2x88x921) hydorcarbyl radical is a cyclododecyl group. Hereafter this compound is referred to for convenience as Me2Si(C5Me4)-(NC12H23)TiQ2.
The alumoxane component of the catalyst system is an oligomeric compound which may be represented by the general formula (R3xe2x80x94Alxe2x80x94O)m which is a cyclic compound, or may be R4(R5xe2x80x94Alxe2x80x94Oxe2x80x94)mxe2x80x94AlR62 which is a linear compound. An alumoxane is generally a mixture of both the linear and cyclic compounds. In the general alumoxane formula R3, R4, R5 and R6 are, independently a C1-C5 alkyl radical, for example, methyl, ethyl, propyl, butyl or pentyl and xe2x80x9cmxe2x80x9d is an integer from 1 to about 50. Most preferably, R3, R4, R5 and R6 are each methyl and xe2x80x9cmxe2x80x9d is at least 4. When an alkyl aluminum halide is employed in the preparation of the alumoxane, one or more R3-6 groups may be halide.
As is now well known, alumoxanes can be prepared by various procedures. For example, a trialkyl aluminum may be reacted with water, in the form of a moist inert organic solvent; or the trialkyl aluminum may be contacted with a hydrated salt, such as hydrated copper sulfate suspended in an inert organic solvent, to yield an alumoxane. Generally, however prepared, the reaction of a trialkyl aluminum with a limited amount of water yields a mixture of both linear and cyclic species of alumoxane.
Suitable alumoxanes which may be utilized in the catalyst systems of this invention are those prepared by the hydrolysis of a trialkylaluminum; such as trimethylaluminum, triethyaluminum, tripropylaluminum; triisobutylaluminum, dimethylaluminumchloride, diisobutylaluminumchloride, diethylaluminumchloride, and the like. The most preferred alumoxane for use is methylalumoxane (MAO). Methylalumaxanes having an average degree of oligomerization of from about 4 to about 25 (xe2x80x9cmxe2x80x9d=4 to 25), with a range of 13 to 25, are the most preferred.
Catalyst Systems
The catalyst systems employed in the method of the invention comprise a complex formed upon admixture of the titanium metal component with an alumoxane component. The catalyst system may be prepared by addition of the requisite titanium metal and alumoxane components to an inert solvent in which olefin polymerization can be carried out by a solution, slurry or bulk phase polymerization procedure.
The catalyst system may be conveniently prepared by placing the selected titanium metal component and the selected alumoxane component, in any order of addition, in an alkane or aromatic hydrocarbon solventxe2x80x94preferably one which is also suitable for service as a polymerization diluent. Where the hydrocarbon solvent utilized is also suitable for use as a polymerization diluent, the catalyst system may be prepared xe2x80x9csin situxe2x80x9d in the polymerization reactor. Alternatively, the catalyst system may be separately prepared, in concentrated form, and added to the polymerization diluent in a reactor. or, if desired, the components of the catalyst system may be prepared as separate solutions and added to the polymerization diluent in a reactor, in appropriate ratios, as is suitable for a continuous liquid phase polymerization reaction procedure. Alkane and aromatic hydrocarbons suitable as solvents for formation of the catalyst system and also as a polymerization diluent are exemplified by, but are not necessarily limited to, straight and branched chain hydrocarbons such as isobutane, butane, pentane, hexane, heptane, octane and the like, cyclic and alicyclic hydrocarbons such as cyclohexane, cycloheptane, methylcyclohexane, methylcycloheptane and the like, and aromatic and alkyl-substituted aromatic compounds such as benzene, toluene, xylene and the like. Suitable solvents also include liquid olefins which may act as monomers or comonomers including ethylene, propylene, 1-butene, 1-hexene and the like.
In accordance with this invention optimum results are generally obtained wherein the titanium metal compound is present in the polymerization diluent in a concentration of from about 0.0001 to about 1.0 millimoles/litre of diluent and the alumoxane component is present in an amount to provide a molar aluminum to transition metal ratio of from about 1:1 to about 20,000:1. Sufficient solvent should be employed so as to provide adequate heat transfer away from the catalyst components during reaction and to permit good mixing.
The catalyst system ingredientsxe2x80x94that is, the titanium metal component, the alumoxane, and polymerization diluentxe2x80x94can be added to the reaction vessel rapidly or slowly. The temperature maintained during the contact of the catalyst components can vary widely, such as, for example, from xe2x88x92100xc2x0 to 300xc2x0 C. Greater or lesser temperatures can also be employed. Preferably, during formation of the catalyst system, the reaction is maintained within a temperature of from about 25xc2x0 to 100xc2x0 C., most preferably about 25xc2x0 C.
Polymerization Process
In a preferred embodiment of the process of this invention the catalyst system is utilized in the liquid phase (slurry, solution, suspension or bulk phase or combination thereof), high pressure fluid phase or gas phase polymerization of an olefin monomer. These processes may be employed singularly or in series. The liquid phase process comprises the steps of contacting an ethylene and an xcex1-olefin monomer with the catalyst system in a suitable polymerization diluent and reacting the monomers in the presence of the catalyst system for a time and at a temperature sufficient to produce an ethylene-xcex1-olefin copolymer of high molecular weight.
The monomers for such process comprise ethylene in combination with an xcex1-olefin having 3 to 20 carbon atoms for the production of an ethylene-xcex1-olefin copolymer. It should be appreciated that the advantages as observed in a ethylene-xcex1-olefin copolymer produced with a catalyst system of this invention would also be expected to be obtained in a copolymer of different xcex1-olefins wherein ethylene is not used as a monomer as viewed in comparison to a copolymer of the same or different xcex1-olefins produced under similar polymerization conditions with a catalyst system which does not use a monocyclopentadienyl titanium compound as defined herein. Accordingly, although this invention is described with reference to an ethylene-xcex1-olefin copolymer and the advantages of the defined catalyst system for the production thereof, this invention is not to be understood to be limited to the production of an ethylene-xcex1-olefin copolymer, but instead the catalyst system hereof is to be understood to be advantageous in the same respects to the production of a copolymer composed of two or more C3 or higher xcex1-olefin monomers. Copolymers of higher xcex1-olefin such as propylene, butene, styrene or higher xcex1-olefins and diolefins can also be prepared. Conditions most preferred for the homo- or copolymerization of ethylene are those wherein ethylene is submitted to the reaction zone at pressures of from about 0.019 psia to about 50,000 psia and the reaction temperature is maintained at from about xe2x88x92100xc2x0 to about 300xc2x0 C. The aluminum to titanium metal molar ratio is preferably from about 1:1 to 18,000 to 1. A more preferable range would be 1:1 to 2000:1. The reaction time is preferably from about 10 seconds to about 1 hour.
The xcex1-olefin to ethylene molar ratio often bears importantly upon the production capacity of a reactor of any designxe2x80x94i.e., whether for solution or gas phase production, etc.xe2x80x94for production of an ethylene based copolymer (i.e.xe2x80x94a copolymer the molar ratio of which is 50% or greater ethylene). The more ethylene input to a reactor in a given unit of time, the greater will be the amount of ethylene based copolymer product obtained in that same unit of time. Yet, polymers are designed for a variety of end services and this design constraint dictates the molar percentage of incorporated xcex1-olefin which must be obtained in the targeted copolymer product. The xe2x80x9ccatalyst reactive ratio (r1)xe2x80x9d of a catalyst system defines the property of the system of assimilating an ethylene monomer into a polymer molecule chain in preference to a particular xcex1-olefin comonomer. The larger the r1 number, the greater the preference of the catalyst system for incorporating an ethylene monomer rather than a xcex1-olefin monomer. Thus, to achieve a targeted xcex1-olefin monomer incorporation (cxcex1) in the product polymer, the higher the r1 value of a catalyst system, the larger must be the Cxcex1/C2 molar ratio of monomers used in the reactor, and as the Cxcex1/C2 ratio increases the lower is the production capacity of the reactor.
To achieve a desired level of xcex1-olefin monomer incorporation in a copolymer product, as can be seen, it is often desired to have a catalyst system which can achieve a low molar ratio of Cxcex1/C2, i.e., a catalyst system with a low r1 is desired. For example, with reference to 1-butene, the catalyst systems of this invention wherein the titanium metal compound has a tetramethyl substitute cyclopentadienyl ligand generally exhibit an r1 value of 6 or less, and typically of 5 or less. Thus, with catalyst systems of this invention an xcex1-olefin incorporation of greater than 20 wt. % can be achieved at a Cxcex1/C2 ratio of 2.0 or less, and typically of about 1.6.
In addition to the benefits of increased reactor productivity which, for a copolymer of a targeted xcex1-olefin incorporation level, which a catalyst system of lower r1 values allows, other significant additional benefits ensue from a low r1 value. Recovery of unreacted monomer, particularly xcex1-olefin monomer for later reuse adds significantly to production cost. By use of the catalyst systems. identified by this invention, the cost of unreacted xcex1-olefin monomer recovery may be reduced significantly since a smaller quantity of xcex1-olefin monomer can be used to achieve the same target level of xcex1-olefin incorporation.
Further, since it is the ratio of Cxcex1/C2 in the medium wherein polymerization occurs which is critical (i.e., liquid phase, gas phase, or super critical fluid phase, etc.) the low r1 values for the catalyst systems of this invention permit the catalyst systems to be used in a wider variety of polymerization procedures than was heretofore believed to be practically possible. Praticularily within this range of possibilities is that of the gas phase polymerization of an ethylene xcex1-olefin copolymer of a greater than heretofore believed possible level of xcex1-olefin incorporation.
Without limiting in any way the scope of the invention, one means for carrying out the process of the present invention for production of a copolymer is as follows: in a stirred-tank reactor liquid xcex1-olefin monomer is introduced, such as 1-butene. The catalyst system is introduced via nozzles in either the vapor or liquid phase. Feed ethylene gas is introduced either into the vapor phase of the reactor, or sparged into the liquid phase as is well known in the art. The reactor contains a liquid phase composed substantially of liquid xcex1-olefin comonomer, together with dissolved ethylene gas, and a vapor phase containing vapors of all monomers. The reactor temperature and pressure may be controlled via reflux of vaporizing xcex1-olefin monomer (autorefrigeration), as well as by cooling coils, jackets etc. The polymerization rate is controlled by the concentration of catalyst. The ethylene content of the polymer product is determined by the ratio of ethylene to xcex1-olefin comonomer in the reactor, which is controlled by manipulating the relative feed rates of these components to the reactor.
As before noted, a catalyst system wherein the Group IV B transition metal component is titanium has the ability to incorporate high contents of xcex1-olefin comonomers. Accordingly, the selection of the titanium metal component to have the cyclopentadienyl group to be tetramethyl substituted and to have an amido group bridged through its nitrogen atom to the cyclopentadienyl ring wherein the nitrogen of the amido group is bonded through a 10xc2x0 or 2xc2x0 carbon atom to an aliphatic or alicyclic hydrocarbyl group, most preferably an alicyclic hydrocarbyl group is another parameter which may be utilized as a control over the xcex1-olefin content of the ethylene-xcex1-olefin copolymer within a reasonable ratio of ethylene to xcex1-olefin comonomer. For reasons already explained, in the production of an ethylene-xcex1-olefin copolymer a molar ratio of ethylene to xcex1-olefin of 2.0 or less is preferred, and a ratio of 1.6 or less is more preferred.